The invention relates to a lever and latch in a safety mechanism for a plastic injection molding machine having a safety gate.
A safety gate insures that an operator does not extend his hand or other portion of his body into a dangerous position between the mold halves whenever the machine hydraulic pumps and control valves are in a condition to close the mold. Since the forces involved are considerable, if an operator's hand or other parts of his body are caught between the mold halves, the injury which is incurred is severe. Various safety mechanisms have been devised in order to insure that the hydraulic control valves which control the functions of the machine are deenergized whenever the safety gate is slightly opened. Such safety mechanisms normally take the form of limit switches and hydraulic valves which sense the closed or open position of the safety gate and deenergize the control valves whenever the gate is open. While such mechanisms should prevent accidents, the switches and the valves may become defective and in some instances, in order to save time and to increase the output of the machine, operators tamper with such devices, rendering them inoperative.
One solution to this problem has been achieved by the mechanical safety mechanism disclosed in U.S. Pat. No. 3,386,133 issued on June 4, 1968. In that patent, there is disclosed a mechanical linkage connected between the safety gate and a guide rod which is secured to the movable platen. Whenever the safety gate is slightly opened, a pawl is inserted into a notched guide bar in order to restrain the movable platen against advance. A second solution is shown by U.S. Pat. No. 3,728,057 issued on Apr. 17, 1973. In that patent, a movable platen is steadied by one or more guide bars, at least one of which has notches or other stop members thereon. A pawl is engaged with the guide bar for physically preventing the advance of the movable platen, and mechanical linkage is connected between the pawl and the safety gate, which linkage includes a torque shaft. Movement of the safety gate rotates the torque shaft to control the positioning of the pawl with respect to the guide bar.